The present invention relates to a sizer for implantable prosthetic heart valves. More particularly, the present invention relates to a sizer for more precisely determining the proper size of a prosthetic heart valve to be implanted during heart valve replacement surgery.
Various types and configurations of prosthetic heart valves, used to replace diseased natural human heart valves, are known in the art. The actual shape and configuration of any particular prosthetic heart valve is, of course, dependent to some extent upon the valve being replaced (i.e., mitral valve, tricuspid valve, aortic valve, and pulmonary valve). In general terms, however, the prosthetic heart valve design attempts to replicate the function of the valve being replaced and thus will include valve leaflet like structures. With this in mind, prosthetic heart valves including valve leaflets are generally categorized as either forming relatively flexible leaflets or relatively rigid leaflets.
The category including prosthetic heart valves which form relatively flexible leaflets includes bioprosthetic heart valves having leaflets made of a biological material as well as prosthetic heart valves having leaflets made of synthetic (e.g., polymeric) material. Flexible leaflet prosthetic heart valves are generally categorized as having a frame or stent or as having no stent. The stent in a stented prosthetic heart valve normally includes a substantially circular base or stent ring around which an annular suture material is disposed for suturing the prosthesis to heart tissue. The stent ring including the annular suture material is typically referred to as a sewing ring. Further, the stent forms at least two, typically three, support structures extending from a stent ring. The support structures are commonly referred to as stent posts or commissure posts and include an internal, rigid yet flexible structure extending from the stent ring, covered by a cloth-like material similar to that of the annular suture material. The stent or commissure posts define the junction between adjacent tissue or synthetic leaflets otherwise secured there too.
Examples of prosthetic heart valves are described in U.S. Pat. No. 4,106,129 to Carpentier et al. and U.S. Pat. No. 5,037,434 to Lane, the teachings of which are incorporated herein by reference. These disclosures detail a conventional configuration of three leaflets wherein one leaflet is disposed between each pair of stent or commissure posts. The Hancock® Modified Orifice Aortic Bioprosthesis and the Hancock® II Bioprosthesis, both manufactured by Medtronic, Inc., Minneapolis, Minn., are commercially available examples of bioprosthetic valves. Both the Hancock® Modified Orifice Bioprosthesis and the Hancock® II are available in various sizes such that they may be implanted in patients having corresponding varying sizes of heart valve annuli.
Prosthetic heart valves categorized as forming relatively rigidly leaflets include mechanical prosthetic heart valves. A typical mechanical heart valve includes an annular valve housing or body to provide a passageway for blood flow. Relatively rigid leaflets are rotatably mounted to the annular housing and rotate to open or close the blood flow passageway. The Medtronic Hall® mechanical heart valve, manufactured by Medtronic, Inc., Minneapolis, Minn., is a commercially available example of a mechanical heart valve. Similar to bioprosthetic valves, mechanical heart valves are available in various sizes such that they may be implanted in patients having corresponding varying sizes of heart valve annuli.
During valve replacement surgery, the heart valve prosthesis, whether it be a bioprosthesis or a mechanical heart valve, is implanted within the patient's heart either in a supra-annular or intra-annular implant technique. The supra-annular implant technique sutures the prosthetic heart valve above the annulus corresponding to the heart valve to be replaced. The intra-annular implant technique sutures the prosthetic heart valve within the annulus corresponding to the heart valve to be replaced.
Ideally, the heart valve annulus is formed of relatively healthy tissue receptive to some shaping by the surgeon in preparation of receiving the heart valve prosthesis. However, due in part to the space and time constraints during valve replacement surgery, the shape of the resulting annulus is often less than perfect for the attachment of a heart valve prosthesis. At times, the annulus and/or the patient's natural leaflets are calcified, requiring complete annular debridement or removal of the hardened tissue. The annular debridement results in a less defined annulus ledge and larger overall orifice into which, or above which, the prosthetic heart valve is to be attached. As such, the size and contour of each annulus varies widely from patient to patient.
Due to the uneven nature of the annuli, it is crucial that a surgeon select a properly sized prosthetic heart valve to match a particular patient's annulus. Typical annulus sizers are simple cylinders made out of rigid plastics, wherein the cylinder diameter corresponds to a size of a particular prosthetic heart valve. During surgery, a surgeon typically has a number of sizers at his or her disposal, each sizer having a different size or diameter (i.e., each sizer relating to a different size of prosthetic heart valve). A surgeon inserts the sizer or a series of different sizers into the valve opening to measure the size of the valve opening. Upon determining the size of the valve opening, the surgeon selects a heart valve prosthesis for implantation having a size believed to correspond to the size of the valve opening.
Although typical annulus sizers are rigid, the sewing or attachment ring included on prosthetic heart valves are flexible. When inserted within or above the valve annulus, the sewing ring compresses and conforms more closely to the heart valve annulus. Where the selected heart valve prosthesis has a diameter substantially identical to the rigid sizer otherwise found to best “match” the annulus, this compression or conformity may result in the selected prosthetic heart valve being too small for the valve opening or annulus. Other times, a heart valve prosthetic sized to fit the valve opening may be too large for attachment to an unusually small annulus ledge. Accordingly, typical prosthetic heart valve sizers often erroneously suggest the size of prosthetic heart valve to be implanted. In such a case, the selected prosthetic heart valve is discarded and a new prosthetic heart valve is chosen. Not only is this a waste of the relatively expensive valve prosthesis, but it is also a waste of time, which is often critical to the patient's well being in valve replacement surgery. Therefore, in light of the above, a need exists for a prosthetic heart valve sizer that more accurately represents the actual size and flexibility of the prosthetic heart valve to be implanted.